Bridging alkyls in d-transition metal chemistry: Reactions of (cod) 2M2(μ-R)2 with organolithium reagents to give (cod)2M2(R)4Li2, where M is Rh or Ir, and the crystal structure of (cod)2Rh2(CH2SiMe3)4Li2 and (cod) Rh( CH2SiMe3)2Li(Me2NCH2CH2NMe2)